Randolph · Norfolk County

Can you build an ADU in Randolph?

Randolph's Building Department publishes a plain-language ADU FAQ, and it answers the question that decides most South Shore deals: what happens to the apartment that is already in the basement. A unit built before February 2025 needs a recorded special permit to be legal, or it starts over.

What the state guarantees you

Since 2 February 2025 this applies in every Massachusetts community. A town may be more generous than this. It may not be less.

Rule	What it means
Allowed by right	One ADU in single-family zoning districts, statewideNo special permit and no public hearing for a protected-use ADU
Maximum size	900 sq ft, or 50% of the principal dwelling, whichever is smallerA town may allow larger. It cannot allow smaller
Owner occupancy	A town cannot require itSo you may rent both units, or live in the ADU and rent out the house
Parking	One space at most, and none at all within half a mile of transitA town cannot ask for more than this
Short-term rental	The state leaves this to each townAll six towns documented here ban it, and two of them ban it for the main house too
In force since	2 February 2025Any conflicting local zoning became unenforceable that day

What Randolph adds on top

Rule	In Randolph
Where allowed	Within, attached to, or detached from a single-family home
Maximum size	50% of the main house or 900 sq ft, whichever is smaller
Owner occupancy	Not required. No restriction on who may live in either unit
Short-term rental	Prohibited, for the ADU and the main house
Where you file	Randolph Building Department
What it costs to file	Building permit, electrical and plumbing fees, inspection fees, and water and sewer connection fees charged per bedroom
A unit built before Feb 2025	Needs a special permit granted by the town and recorded at the Norfolk County Registry
Without that record	You file a fresh building permit with architectural plans showing the unit meets current code

That last pair of rows is the reason to read this page before you make an offer. A great many South Shore single-families were turned into two-units decades ago, and the listing will call it an in-law or a bonus room. If there is no recorded special permit, you are not buying a legal two-unit, you are buying a single-family and a code problem. Sometimes it can be brought into compliance under the new law, which is worth real money. Sometimes the ceiling height or the egress makes that impossible. Establish which before the offer, not during the inspection. Note also that the short-term rental ban reaches your own house, not just the ADU.

Questions people ask

How big can an ADU be in Randolph?

No larger than 50% of the main home or 900 square feet, whichever is smaller.

Does Randolph require the owner to live on the property?

No. Randolph states there are no restrictions on who may live in the ADU or the main residence, which follows the state prohibition on owner-occupancy requirements.

I am buying a Randolph house with an existing in-law apartment. Is it legal?

Only if a special permit was granted by the town and recorded at the Norfolk County Registry of Deeds. If no such record exists, the unit is not permitted, and legalising it means a fresh building permit application with architectural plans showing it meets current code. Check the registry before you make an offer.

Can I list a Randolph ADU on Airbnb?

No. Neither the ADU nor the main house may be used as a short-term rental.